The direct receptor binding technique was chosen to study adrenergic receptors in the pulmonary vasculature as a first step in characterizing the pharmacological and functional characteristics of these receptors under normal and abnormal conditions. Studies began with examination of ligand binding to beta-adrenergic receptors in rabbit whole lung membranes. L-(3H)-Dihydroalprenolol (DHA), a reversible, non-selective beta-adrenergic receptor antagonist, was chosen as the radioligand. The fundamental characteristics of DHA binding to whole lung membranes have been demonstrated, including kinetics, high affinity, saturability, specificity and stereospecificity. More detailed characteristics of pulmonary beta-adrenergic receptors are also under investigation. Using these results as a basis, beta-adrenergic receptor binding in pulmonary blood vessels will be examined in a similar manner, both under normal circumstances and under conditions which are known to alter pulmonary vascular reactivity to investigate the involvement of adrenergic receptors in these responses of pulmonary vasculature.